Generally, the front-end circuit of such an RF electronic device comprises at least one amplifier coupled at the output or at the input to an antenna to respectively transmit or receive an RF signal.
In transmission, the amplifier or amplifiers coupled at the output to the antenna are typically power amplifiers.
In reception, the amplifier or amplifiers coupled at the input to the antenna are typically low-noise amplifiers (LNAs).
If, for example, the transmission side is considered, each power amplifier of the RF electronic device receives, at its input, an input signal with a low amplitude and then delivers, in an ideal case, at its output to the antenna, an output signal which is an amplified image of the input signal.
In order to allow a maximal transfer of power between the transmission path and the antenna, it is desirable to ensure a matching of the antenna to the amplifier in terms of their respective impedances. In other words, it is desirable for the impedance of the antenna to be equal to the optimal impedance to be exhibited at the output of the amplifier to avoid reflections.
In this respect, a standing wave ratio (SWR), or more specifically “VSWR” (voltage standing wave ratio), is generally used to assess the quality of the matching of the antenna to the amplifier.
When the impedances of the antenna and of the amplifier are matched, all the power of the output signal is delivered to the antenna. There is therefore no wave reflection and the voltage standing wave ratio VSWR is 1, i.e. the minimal value.
When the ratio VSWR becomes greater than 1, the impedances of the antenna and of the amplifier are no longer matched. Consequently, there is a wave reflected from the antenna to the amplifier.
This impedance mismatch consequently causes a reduction on the electrical power delivered to the antenna and a degradation of the performance levels of the power amplifier. Furthermore, this reflected wave will be able to negatively influence the reliability of the amplifier.
Conventional circuits for detecting wave reflection and voltage standing wave ratio VSWR levels between an antenna and a power amplifier require a direct implementation between the antenna and the amplifier together with correction circuits for modifying the impedance of the antenna so as to match any change of the impedance of the antenna. This implementation inevitably presents insertion losses at the output of the amplifier, which reduces the performance of the power amplifier.
The drawbacks which have just been described for an amplifier of a transmission chain can be transposed to an amplifier of a reception chain.
There is thus a need to propose a technical solution of low complexity that makes it possible to detect the level of impedance matching between the amplifier and the antenna, whether in transmission and/or in reception, in particular via the VSWR ratio, without introducing therein insertion losses and to rematch the impedance of the output of the amplifier to that of the antenna when there has been a variation of impedance on the latter.